The present invention relates generally to injection molding systems and, more particularly, to an injection molding modular manifold system having a plurality of internally heated components which can be assembled together in an interconnected fashion to form a heated melt distribution passage which leads from an injection molding machine nozzle to any number of mold cavity gates.
Injection molding is commonly used to produce a number of plastic items. It is beneficial to the molding manufacturer to produce multiple products with every "shot", or cycle, of the injection molding machine, rather than molding one individual product per molding cycle. When multiple parts are molded in each cycle, such parts are commonly interconnected by solidified plastic and form a "runner" which interconnects the multiple parts. The individual parts must then be trimmed from their runners which requires additional labor and creates material waste. Runnerless injection molding is used to eliminate the necessity of trimming the plastic runner before subsequent further assembly or packaging of the products.
In order to take advantage of the efficiency of runnerless injection molding, it is required that the melt pathway between the injection molding machine and the mold cavity gates positioned in the mold block or blocks be heated. To achieve the desired heating of substantially the entire melt pathway, a variety of individually heated members such as sprue bushings, torpedoes and/or cartridge heaters have been developed. Using heated members requires either that the heated members themselves be arranged in such a manner to form a substantially continuous heated flowpath from the injection entry point to each mold cavity gate or requires the heated manifold be present to provide a heated melt pathway for the injected melt leading from the injection molding machine nozzle to the various secondary heated members and/or to the mold block cavity gates.
Typically, these manifolds have taken the form of relatively large elongated heated plates, such as is described in U.S. Pat. No. 4,761,343, in which a plurality of secondary heating elements are disposed in respective mold cavity gate passageways and which are interconnected to an injection molding machine heated nozzles by means of a series of elongated plates. These elongated plates take up much room within the mold blocks and require a complex heating element insert system. Additionally, plate-type manifolds are, because of their mass, require more energy to heat up the plate and are further subject to greater thermal expansion than the secondary heated members which they engage, thereby necessitating modification of both the secondary heated members and the manifold plates to take into account the forces encountered in such expansion. This problem is aptly described in U.S. Pat. No. 4,433,969. Moreover, such plate-type manifolds are relatively large and virtually require a uniquely designed manifold plate for every molding layout, thereby necessitating that the molding manufacturer maintain a large inventory of manifold plates.
Thus, a need in the art exists for a modular injection molding manifold system. Some manifold systems are modular in nature and alleviate some of the above-referenced disadvantages. An example of such a manifold system is the True Shot.RTM. runnerless injection molding system described in the National/Rama Corporation Brochure dated October, 1989. Although the system shown therein describes a plurality of interconnecting components, the interconnecting manifold components are externally heated by numerous external band heaters. The use of external band heaters has certain disadvantages. The outer surfaces of the band heaters are exposed to the air, and thus not all of the heat provided by the band heater is applied to the manifold component it encircles, because some of the heat escapes, by radiation, to the air and the mold plates surrounding the component. This heat loss raises the power requirement necessary to maintain the manifold system at the desired temperature. Moreover, external band heaters are limited in their length and thus do not evenly heat the entire length of the manifold component to which the band heater is applied. Furthermore, because the band heaters are applied to the outer surface of the manifold components, they are subject to thermal expansion when energized, which may result in the band heater "growing" away from the manifold component it is applied to. Consequently, the band heaters cannot be adjusted after they are energized to correct this growth. Thus, it is evident that band heaters do not provide an even heat distribution to a series of interconnected manifold components.
Accordingly, there remains a need in the art for an injection molding manifold system which is internally heated and which is modular in nature such that substantially all of the modular interconnecting manifolds are internally heated.
The present invention is directed to a modular manifold system for use in injection molding which overcomes the aforementioned disadvantages. In this regard the present invention provides a modular manifold system which includes a plurality of internally heated interconnecting components which form a continuous, heated flowpath which leads from the injection molding machine nozzle or bushing, to a plurality of secondary heated members disposed in various mold block openings which lead to the respective mold cavity gate of the molding system.
Each component of the modular manifold system is internally heated by an electrical heating element in the form of a ceramic sleeve which may be disposed in an annular cavity encircling the internal passageway. Each manifold component has an integral construction, meaning that its outer wall, endwall and inner melt passageway sidewall are all formed from a single piece of material providing the manifold component with an integral casing or housing in which no joints, welded or otherwise, are present along the melt flowpath thereby reducing the likelihood of heater failure due to melt infiltration into the internal heating element. Some portions of the manifold component body extend outwardly to contact the mold block surfaces to provide an air gap between the manifold component and the mold block to thereby minimize the amount of heat transferred to the surrounding mold block. Other portions of the manifold component body extend outwardly to provide support surfaces which assist the manifold component in resisting the forces applied thereto by the pressure of the injected melt and hold the manifold component in place.
Accordingly, it is a general object of the present invention to provide a modular manifold system for use in injection molding having a plurality of interconnecting, internally heated manifold components.
Another object of the present invention is to provide a modular manifold system for injection molding having a plurality of internally heated manifold components which, when assembled together, form a heated passageway between a primary heated member and one or more secondary heated members and wherein each manifold component includes an axially extending annular compartment containing a heating element assembly in the form of a sleeve wherein the heating element assembly is disposed within the manifold component in a heat transfer relationship to the internal melt passageway.
A further object of the present invention is to provide a modular injection molding manifold system having a plurality of interconnecting, internally heated manifold modules wherein each of the manifold components has an internally heated inner melt passageway extending through an elongated inner core and wherein each module is substantially of one-piece construction wherein the manifold component outer wall, endwall and melt passageway inner core wall are formed from one piece of material.
It is still another object of the present invention to provide a modular injection molding manifold system having a plurality of internally heated, interconnecting manifold components, which can be interconnected to one another to form a variety of injection molding manifold configurations and which can also be easily disassembled to allow both quick and reliable assembly and disassembly of the manifold system.
It is yet still a further object of the present invention to provide a modular manifold system for injection molding having a plurality of internally heated manifold components wherein each manifold component includes its own temperature sensing and controlling means, thereby allowing the user to monitor and control the temperature of the manifold system from the primary heated member to the secondary heater members.
Yet another object of the present invention is to provide a balanced linear modular manifold system for use in a mold block system with multiple "drops", the system having a plurality of interconnecting, internally heated manifold components wherein the linear distance between the melt distribution element and each "drop" is the same, thereby providing a similar flow distance between the system inlet and all the system "drops" to maintain a uniform pressure drop throughout the manifold system.
Yet still another object of the present invention is to provide an injection molding balanced modular manifold system having a plurality of interconnecting, internally heated manifold components in which the thermal expansion of the manifold components is directed toward the center of the manifold system.
These and other objects, features and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings wherein like reference numerals refer to like parts.